I did not say crosstraining
in dressage is harmful to jumpers or reiners. But if you ride a jumper dressage style, you won't go over fences very well. Nor will you win many races.
Dressage is NOT good basic riding for jumping. Jumping uses a FORWARD seat, not a dressage seat. There is a reason manufacturers make jumping saddles and dressage saddles, rather than nothing but all purpose saddles. If you ride with shoulder / hip / heel aligned, you won't be able to do this:
Not sure why some one who does nothing of these things thinks they have some insite into it. You are bassing everything you are talking about from old pictures and books. It is not about using the same position it is about what you gain from doing other things. Yes you may work in a Dressage position when doing Dressage and a Jumper position when jumping but one is still benificial to the other. Do you think that someone who rides Jumpers can not then turn around and ride in a correct Dressage style? Do you think it is a one of the other? It is not. I show reiners reined cow horses I have roped team pened and cut. I have also run speed events. Each one you ride in a different manner. When I rein I ride as you would when reining. When I rope I ride as a roper would and so on. I find that by doing this I build different muscles and by doing so it helps regardless of what I end up doing with my horse.
Correction: you can jump using something close to a dressage seat. There are some photos from the 1920s I've seen that show the US Army jumping that way, in a partial dressage seat, and it wasn't pretty for horse or rider.
There is a reason for different styles of riding. No one style is the basis of all others. Heck, dressage isn't all that old, either. The Mongols were good horsemen, but they didn't practice dressage. Nor did the Comanches, for that fact. Yes there is nothing that says you can only do one or the other. You do know it is posible to do many differnet things. I use to play a lot of different sports in school. All at a varsity. They where are quite different in what was needed. You just have to understand that change what needs to be changed and use what you may have learned from one to use in anouther.
If dressage was the basis for all good riding, we would all want to ride like dressage riders. If dressage was the basis for all good riding, we would all want to breed dressage horses. We don't, because 'different horses for different courses'. Texas cowboys don't do a degraded form of dressage. They ride horses. Jockeys don't use a degraded form of dressage. The forward seat is not a deformed method of riding.
What can be controversial about saying that there is more than one way to ride well, and that dressage doesn't define the only way to ride?
I've said my piece. I've tried to be clear. I've tried to keep some humor and even toss some oil on boiling waters at times. If folks want to believe that dressage defines good riding, they will. But I've yet to hear anyone explain how a forward seat evolved from dressage, or how come those old time Texas cowboys (and Arizona guys too) got the job done without ever reading the "masters". I also haven't heard an explanation for why the US Cavalry investigated collected riding - those same European masters - and REJECTED it as harmful to the goals of military riding.